Conventional electronic products that have a display such as notebook computers, PDAs, digital cameras, mobile phones and the like generally have a hinge to axially couple the display and a host body on two opposite sides thereof. When in use, the display is unfolded relative to the host body. When not in use, the display may be folded over the host body in a closed manner to make stowing and carrying easier.
To fully close the display and the host body after folded, a hook usually is provided to latch the display. For instance, R.O.C. patent No. 506549 discloses an inclined hinge with a torque difference. The hinge has an installation element installed on a metal portion of one side of the body with a metal bearing bent vertically, a swivel portion installed on one side of an opening/closing body and having an installation portion, a larger diameter portion and a deformed smaller diameter portion that are mounted onto the metal bearing so that a pintle can be pivoted about a bearing hole. The pintle is held in a hole formed in the center between the greater diameter portion and one side of the metal bearing. A first friction pad is provided to pivot concurrently with the pintle or stop the metal bearing with a central aperture inserted by the deformed smaller diameter portion. There is a second friction pad fastened to the metal bearing or pivoted concurrently with the pintle. A deformed insert hole is formed in the center of the contact location between the first and second friction pads to hold the deformed smaller diameter portion. One or more than one compression spring washers, discs or undulate blades are provided to form an elastic means. The connection is made when the deformed smaller diameter portion is inserted into a hole formed in the center of the elastic means. A depressing pad is provided to pivot concurrently with the pintle, and driven by the deformed smaller diameter portion, and the pintle has a protrusive side. The metal bearing can generate different friction torques axially on any side due to the pivoting angle of the pintle.
However, during swiveling displacement for closing, it does not provide a hinge of automatic and closed folding of the display over the host body while the pintle is pivoted to a selected angle. It still has drawbacks. To remedy the aforesaid disadvantage, R.O.C. patent No. 411069 entitled “Hinge” provides an adjustment structure with a turning displacement formed between a joined surface of a rotary member and an anchor member. At one selected spot, the rotary member and the anchor member can be latched to form a stageless anchoring and closing without opening or closing the display. By adding a resistance generation structure equipped with a resistance element and a washer, the mutual friction resistance between them also can increase. Hence it provides a steadier stageless anchoring and closing even with a hinge of a smaller diameter. While the R.O.C. patent No. 411069 can provide automatic closing, it still leaves a lot to be desired. More details of its deficiencies are elaborated as follow by referring to FIGS. 1A through 1E and FIG. 2.
FIG. 1A is a fragmentary schematic view of R.O.C. patent No. 411069 and the twisting force curves while it is in consecutive actions. It includes an anchor member 5, a rotary member 6, a resistance generation structure 9 and a returning element 8 interposed between the rotary member 6 and the resistance generation structure 9. The positional relationship of the anchor member 5, rotary member 6, returning element 8 and resistance generation structure 9 shown in FIG. 1A represents a condition of the display fully folded over the host body (not shown in the drawings). Referring to FIG. 2, a conventional opening curve (POP) and closing curve (PCL) start at a spot where the display is fully folded over the host body, the pintle pivots at an angle of 0.degree, and the rotary member 6 is elastically pressed by the returning element 8 and slides automatically in a retaining trough 5a of the anchor member 5 so that a twisting force (or an internal stress, with the twisting force at a scale about 1) is formed on the hinge. When the display is unfolded to form an angle of 5.degrees with the host body (i.e. the pintle pivots to 5.degrees), referring to FIG. 1B, a bulged portion 6a slides out through a sloped surface 5b of the retaining trough 5a, and the retaining trough 5a slides to compress the returning element 8, as a result the twisting force increases rapidly as shown in FIG. 2 by the conventional POP at the angle of 5.degrees. As shown in the drawings, the conventional POP is steep; hence unfolding the display requires a greater force. It means a heavy opening. When the display is opened to form an angle just over 10.degrees with the host body (i.e. the pintle pivots just over 10.degrees), referring to FIG. 1C, the bulged portion 6a has fully slid out of the sloped surface 5b of the retaining trough 5a, and compresses the returning element 8 and passes over a threshold point, as a result a maximum twisting force is formed on the returning element 8 caused by the maximum compression of the bulged portion 6a, then drops drastically as shown in FIG. 2 by the conventional POP at the angle over 10.degrees. Thus during unfolding of the display, the maximum twisting force (at a scale about 8) of the conventional POP of the hinge is quite significant, namely for the conventional display equipped with the automatic closing hinge, unfolding the display needs a greater force. This is the main drawback of the R.O.C. patent No. 411069. As a result, unfolding the display from the host body often requires a user prying with two hands. Otherwise the host body tends to be dragged to the display during the unfolding process. However, after the display has been unfolded to form an angle over 10.degrees with the host body (i.e. the pintle has pivoted over 10.degrees), referring to FIGS. 1D and 1E, the bulged portion 6a has already escaped the sloped surface 5b without continuously compressing the returning element 8, and slides to form a steady twisting force (at a scale about 4.5) as shown in FIG. 2, indicated by the conventional POP. On the other hand, when the display is closed to form an angle with the host body just over 10.degrees (i.e. the pintle pivots just over 10.degrees), referring to FIG. 1C, the bulged portion 6a is compressed by the returning force of the returning element 8, and has just passed over the threshold point and starts to slide into the retaining trough 5a through the sloped surface 5b to return to the position shown in FIG. 1A. Also referring to FIG. 2, then a conventional closing curve (PCL) is formed while the pintle pivots within an angular range between 10.degrees and 0.degree. When the display closes at the selected angle of 10.degrees on the conventional PCL, a steady twisting force (at about a scale of 4.5 against the compressing force of the returning element) is formed to automatically fold the display over the host body to generate a “light closing” result. Consequently, the closed display also receives a smaller depressed force. This is another problem occurred to R.O.C. patent No. 411069.